152 RESEARCHES ON FUNGI 



organisation in which some individuals of a species (the spore-hke 

 cells) are sacrificed for the good of others (the ordinary spores) 

 which may develop further and keep the species in existence. 



The Phycomycetes. — In the lower Fungi there are many species, 

 e.g. Mucor mucedo (Fig. 84), Pilobolus longipes, and Saprolegnia 

 ferax, in which, apart from the requirements of sex, the individual 

 mycelia never unite but live to themselves alone, no social organisa- 

 tion being displayed.^ 



The Hymenomycetes. — In the Hymenomycetes — the leading 

 group of the Higher Fungi — non-sexual hyphal fusions between 

 hyphae of the same mycelium, or between hyphae of two or more 

 mycelia of the same species, have long been known and can readily 

 be observed in hanging-drop cultures. Often, in larger cultures 

 inoculated with many spores of a single species, the myceUa all 

 unite to form a large compound mycehum, and then this complex 

 netted thallus acts as a unit in the formation of one or more large 

 fruit-bodies. This social organisation, hitherto, has not received 

 the attention which it deserves ; but it must frequently come into 

 play in Hymenomycetes hving under natural conditions and be of 

 considerable importance in aiding the survival of all those species 

 which exhibit it. 



Hyphal Fusions and Clamp-connexions in the Hymenomycetes. 

 — In preparation for a more complete discussion of social organisa- 

 tion in the Hymenomycetes, a few words must here be said about 

 the origin and nature of their hyphal fusions and clamp-connexions. 

 The union of two separate hyphae with one another in the 

 Hymenomycetes takes place in two ways, with results which have 

 already been illustrated for the mycehum of Panus stypticus in 

 Volume III. 



( 1 ) In the older part of a mycelium a branch hypha may develop 

 laterally from another hypha in the usual manner. Then, owing 

 to apical growth, its end may happen to come near the side of 



1 It must not be supposed, however, that hyphal fusions between vegetative 

 hyphae are entirely unknown in the Phycomycetes, for they occur in Syncephalis. 

 For illustrations vide W. Zopf, " Zur Kenntniss der Infectionskrankheiten niederer 

 Thiere und Pflanzen," No. IV, Nova Acta Acad. Caes. L.-C. Nat. Cur., Bd. LII, 1888, 

 Taf . 6, Figs. 4, 5. Like Zopf, I have observed hyphal fusions in the mycelium of a 

 Syncephalis parasitic on Pilobolus. 



